Expansion joint for slabs of concrete roadways

ABSTRACT

The invention comprises an improved expansion joint for slabs of concrete roadways which eliminates heat buckling. The transverse ends, instead of being vertical, are molded so as to be mutually sloping so that when the slabs expand under unusual heat condition, one end slides up the slope of the adjacent end and upon cooling slides back to its normal position solely under the influence of gravity.

nited States Patent [1 1 Peach Dec. 3, 1974 EXPANSION JOINT FOR SLABS OF CONCRETE ROADWAYS [76] Inventor: Robert W. Peach, 888 Pine Trail,

Arnold, Md. 21012 [22] Filed: Nov. 29, 1972 [21] Appl. No.: 310,201

[52] US. Cl. 404/50, 14/16 [51] Int. Cl. E0lc 11/04 [58] Field of Search 404/50, 51, 41, 57, 47, 404/39, 70, 17, 53, 54; 14/16; 52/573 [56] 7 References Cited UNITED STATES PATENTS 140,835 7/1873 Kilburn 404/39 1,010,417 12/1911 Farnum 404/47 1,369,161

2/1921 Benson et al. 404/47 1,991,931 2/1935 Kling 404/17 2,069,146 1/1937 Haupt t 14/16 2,078,485 4/1937 Dunham 404/70 X Primary Examiner-Nile C. Byers, Jr. Attorney, Agent, or FirmScrivener, Parker, Scrivener and Clarke [5 7 ABSTRACT The invention comprises an improved expansion joint for slabs of concrete roadways which eliminates heat buckling. The transverse ends, instead of being vertical, are molded so as to be mutually sloping so that when the slabs expand under unusual heat condition,

' one end slides up the slope of the adjacent end and upon cooling slides back to its normal position solely under the influence of gravity.

1 Claim, 3 Drawing Figures PATENTEL BEE 3l9 4 EXPANSION JOINT FOR SLABS OF CONCRETE ROADWAYS This invention relates to concrete roads and pavements and more particularly to an improved expansion joint between slabs of a concrete roadway and a method of constructing concrete roadways employing the improved joint.

Concrete roads are usually constructed of separate, longitudinally aligned moldedslabs, each of which is poured in place .with the vertical ends of the slab spaced slightly away from the end of 'a previously poured slab. After the slabs have set, the joints between their ends are sealed with a thermoplastic sealing material, such as asphalt, sufficient space being left between the slabs to accommodate the expansion thereof due to the normally elevated temperatures of summer. However, when temperatures rise to abnormally high levels, the total expansion of a number of slabs exceeds the combined space between their ends with the result that at certain joints the endsof the'slabs butt up solidly against each other with such immense force that the ends buckle, oftenexplosively, with spalling and pulverization of the slabs extending in both directions from the joint over several feet. Obviously, driving on a road which has been damaged in this manner is dangerous, and satisfactory repairs can only be effected by removing the broken material and pouring fresh concrete, which prolongs the period that a road is impassable due to heat buckling. v

Heretofore', it has been proposed to overcome the problem of heat buckling of concrete slabs by constructing the ends of the slabs obliquely rather than at right angles to the longitudinal axes of the slabs so that as the slabs expand, the oblique ends push against each other to mutually rotate the slabs slightly about a vertical axis. Though in theory this arrangement would prevent heat buckling, it is unsatisfactory in that means must be provided for restoring slabs to their original aligned position when they contract in cool weather, but no inexpensive reliable means for accomplishing this has so far been devised.

The broad object of the present invention is to provide an expansion joint for the ends of concrete slabs which permits heat expansion without buckling while also enabling the slabs to return automatically totheir normal position after they have cooled and contracted.

Another object of the invention is to provide a slab structure and a method of constructing a concrete slab roadway wherein the problems of heat buckling are entirely eliminated.

The invention will now be described with greater particularity with reference to the drawings wherein:

FIG. 1 is a top plan view ofa typical road section constructed of poured concrete slabs;

FIG. 2is an enlarged vertical cross-sectional view taken substantially on the line 22 of FIG. I; and

FIG. 3 is a view similar to FIG. 2, but showing a modifled version of the invention.

Referring now to the drawings, the numeral 10 designates a road composed of slabs l2, 14 which are poured individually in end-to-end and side-by-side relaadjacent slabs into which a sealing material, such as hot asphalt, is poured for the purpose of sealing the joints against frost and dirt and also providing a yielding spacer capable of being extruded from the joints between slabs when the latter move towards each other due to heat expansion. I

In order to prevent damage to the roadway due to buckling caused by heat expansion, as occurs in conventional roadways described above, the present invention eliminates the problem by constructing the slabs 12, 14 with ends which, instead of being vertical and square, mutually slope as shown at 20, 22 in FIGS. 2 and 3. The sloping ends may be formed by the use of a mold whose ends are suitably shaped that the poured slab 12 defines in longitudinal cross-section an elongated parallelogram having a downwardly facing slope at one end 22 overlying in spaced relationship a complementary, upwardly facing slope at the end 20 of a previously poured slab 14. The opposite end ofthe slab 12 has an upwardly facing slope corresponding to end 20 of slab 14. Except for the sloping end formations,

the process of molding the slabs is conventional with the sloping space between the ends being sealed by hot asphalt 24 or other sealing material prepositioned, poured or inserted into the space. When slabs constructed in accordance with the invention are subjected to high summer heat, they expand longitudinally. However, due to the sloping ends, each slab tends to slide up the slope of the adjacent slab without exerting an appreciable longitudinal push on.

the slab, as occurs with slabs having vertical transverse ends. Furthermore, because the end of one slab tends to slide up the end of its neighbor, there can be no accumulated movement of a plurality of slabs working in one direction against a counter-accumulated movement of a plurality of slabs working in the opposite direction. Thus, with the arrangement of the invention, though one end of a slab may rise slightly above mean level of the roadway as detailed hereinafter, this is due almost exclusively to its own expansion and there is no accumulated movement of successive slabs whereby an end may be forced to rise dangerously above the normal roadway level. Though each slab has a natural tendency to expand in both directions, the end having the upwardly sloping face is essentially anchored by friction and the downwardly sloping end of the next adjacent slab so that the resultant expansion is generally in the direction of the end having the downwardly sloping face because that is the direction of least resistance and any movement of the end having the upwardly sloping face would be so slight as to have almost no detectable effect on the total rise of the downwardly facing end of the adjacent slab.

In addition to the foregoing desirable results, it will be apparent that with slabs having sloping transverse ends, when the slabs contract in cool weather one end merely slides down the face of the other end due to gravity and no special provision need be made for returning the slabs to their normal level positions.

As shown in both FIGS. 2 and 3, the ends of the slabs are reinforced top and bottom, as well as along the sloping faces by reinforcing mesh 28 selected and positioned to provide sufficient reinforcement to sustain possible bending stresses in a vertical direction when the end of one slab slides up the face of the adjacent slab. To eliminate the possible tendency of the sharp corner 30 of an expanded end to break off, the end may be truncated by the provision of a slight vertical shoulder 32, as illustrated in FIG. 3.

The following is an example of the magnitude of the rise of a slab end above the normal road level due to elevated temperatures. Taking a typical value for the coefficient of expansion of concrete as 7.9 X at 100 F for a slab 40 feet long, the expansion linearally for a temperature rise of from 32 F to 132 is:

40 x 12 x 7.9 x 10" 0.3792 inch If the slope of the ends is 2 to l, the slab end would rise V4 of the above amount of about three-sixteenths inch. For a slab 60 feet long the rise will be about 0.2844 inch or slightly over one-fourth inch. Even under the extreme ambient heat conditions of the example, the maximum rise is tolerable and, in fact, is usually no higher than the height of an asphalt strip unnder normal temperature conditions. As shown in the drawings, the normal overflow of asphalt as occurs during application thereof extends naturally above the road level, as shown as 34, and when a slab end expands upwardly, the heat which causes this expansion also causes the asphalt to become tacky, so that it rises readily with the slab end and bridges any abrupt bump which might otherwise occur at the joint. The effect of these bumps can be further minimized by orienting the slopes so that they are positioned in the direction of traffic flow, as indicated by the arrows 36.

It will be understood that though an ideal slope for the ends is a 2 to 1 ratio, any other slope can be selected which enables the downwardly facing end of one slab to slide up and down the upwardly facing end of the other without being prevented from doing so by excessive frictional resistance.

What is claimed is:

1. In a roadway comprising concrete slabs laid endto-end relationship each of said slabs having laterally spaced sides, transverse ends, and upper and lower faces, an expansion joint between the ends of adjacent slabs comprising an upwardly facing slope at one end of one slab extending between the upper and lower faces thereof in a unitary plane, a downwardly facing slope at the adjacent end of the next slab annd overlying in complementary relationship the slope of said first slab, said slopes having a predetermined angle relative to a vertical plane enabling the downwardly facing slope to slide up the upwardly facing slope upon thermal expansion of the slabs against each other, and enabling said first slope to slide down said second slope solely under the influence of gravity upon thermal contraction of said slabs, said sloping ends being normally spaced slightly apart with sealing material filling the space between said ends, the upper transverse edge of the end having the downwardly facing slope being truncated and both of said ends being reinforced to'resist bending stresses in a vertical direction. 

1. In a roadway comprising concrete slabs laid end-to-end relationship each of said slabs having laterally spaced sides, transverse ends, and upper and lower faces, an expansion joint between the ends of adjacent slabs comprising an upwardly facing slope at one end of one slab extending between the upper and lower faces thereof in a unitary plane, a downwardly facing slope at the adjacent end of the next slab annd overlying in complementary relationship the slope of said first slab, said slopes having a predetermined angle relative to a vertical plane enabling the downwardly facing slope to slide up the upwardly facing slope upon thermal expansion of the slabs against each other, and enabling said first slope to slide down said second slope solely under the influence of gravity upon thermal contraction of said slabs, said sloping ends being normally spaced slightly apart with sealing material filling the space between said ends, the upper transverse edge of the end having the downwardly facing slope being truncated and both of said ends being reinforced to resist bending stresses in a vertical direction. 